RU2240627C1 - Cold-cathode ion source - Google Patents

Abstract

FIELD: plasma and high-power ion beam generation.

SUBSTANCE: ion source has hollow cathode, igniter electrode, anode grid disposed opposite output aperture of hollow cathode, screen grid electrically connected to anode grid, and main hollow anode with magnetic system mounted on its surface. Gas is admitted to cathode space. Voltage applied between cathode and igniter electrode strikes glow discharge, electrons from its plasma run through anode grid, arrive at main anode space, and are additionally accelerated due to potential difference applied between grid and main anode. Peripheral magnetic field holds injected electrons in main anode space thereby affording generation of dense and uniform plasma in space free from magnetic field. Ions are taken off plasma through holes in screen electrode.

EFFECT: enhanced efficiency at high uniformity of emitting plasma, simplified design, enhanced reliability and service life of ion source.

1 cl, 1 dwg

Description

The invention relates to techniques for plasma production and generation of high current ion beams.

Ion sources are known in which plasma is generated in the anode cavity, on the surface of which there are rows of permanent magnets with variable polarity to create a multipolar magnetic field. Such a field is maximally near the surface of the anode and rapidly decreases toward the center of the system, which ensures the retention of fast electrons in the plasma and the generation of a homogeneous low-noise plasma in the volume of the anode cavity free from the magnetic field. In such basket-type sources, a heated cathode is usually used [1], the disadvantage of which is a limited time when working with chemically active gases. Ion sources are known in which a plasma cathode based on microwave [2] or radio frequency [3] discharges is used, which provides an increase in resource, but significantly complicates and increases the cost of an ion source.

A known ion source based on the injection of electrons from a glow discharge plasma through a small hole tightened by a fine-structure grid into the cavity of a plasma generator in which the main thin-wire anode is installed [4]. A non-self-contained glow discharge with a hollow cathode develops in the cavity of the generator as a result of gas ionization by injected electrons, from which ions are extracted from the plasma. Such a discharge with fast electrons oscillating inside the cathode cavity is capable of generating a uniform plasma at very low gas pressures, however, the ions generated in the plasma generator are approximately uniformly distributed over the surface of the non-self-sustaining cathode, so the fraction of ions extracted from the plasma is small and amounts to about 4% of the discharge current . As a result, the efficiency of such a simple, reliable, and high-resource ion source is low.

The objective of the invention is to increase the efficiency of the ion source while maintaining high uniformity of the emitting plasma, simplicity, reliability and high resource ion source. To do this, in an ion source containing a plasma cathode, the electrode system of which includes a hollow cathode of a glow discharge, a firing electrode and a fine-structure anode grid mounted opposite the outlet of the hollow cathode, and a plasma generator including an main anode and a screen grid with holes for extracting ions, electrically connected to the anode grid and being at a negative potential relative to the main anode, the main anode is in the form of a hollow electrode, from the outside of which is installed magnet system for generating a multipole peripheral magnetic field.

The inventive plasma cathode of an ion source contains a hollow glow-discharge cathode, a firing electrode and an anode grid mounted opposite the hollow cathode output aperture. The ion source plasma generator contains a screen grid electrically connected to the anode grid, and a main hollow anode, on the surface of which a magnetic system is installed, which creates a multipolar magnetic field. Gas is introduced into the cathode cavity and, when voltage is applied between the cathode and the ignition electrode, a glow discharge is ignited, the current of which is closed through the output aperture of the cathode to the anode and screen grids. When a potential is positive with respect to the grids to the main anode, the electrons injected into the cavity of the plasma generator acquire enough energy to ionize the gas. As the potential difference between the main anode and the grids grows, the current of electrons injected from the cathode cavity increases and their ionizing ability increases, as a result, a dense plasma is generated in the cavity of the main anode. The peripheral field created by permanent magnets reflects fast electrons, ensuring their effective energy relaxation in the plasma and the generation of a uniform plasma in the cavity space free from the magnetic field. Ions are extracted from the plasma through the openings in the screen electrode by the field of a space charge layer or by the field of the accelerating gap of ion optics, in case it is necessary to accelerate ions to higher energies.

In the proposed design of the ion source, electron emission is provided by a cold hollow cathode, the resource of which is determined by ion sputtering, depends on the area of the working surface and the mass of the cathode and, if necessary, can be increased to values ≥10 ³ hours. Since the entire current of ions generated in the plasma generator is collected surface of the screen mesh, this allows you to achieve high values of the energy efficiency of the ion source.

The drawing shows the proposed plasma ion emitter. The ion source consists of a plasma cathode and a plasma generator. The plasma cathode electrode system contains a hollow cathode of a glow discharge 1, an ignition electrode 2 and an anode grid of a plasma cathode 3, a plasma generator contains a hollow main anode 5 and a screen grid 4, which is electrically connected to the anode grid 3. A magnetic system 6 is mounted on the surface of the main anode 5 .

The ion source works as follows.

Gas is introduced into the cathode cavity. Between the cathode 1, the ignition electrode 2 and the anode grid 3, voltages are applied and a glow discharge is ignited. The discharge current closes through the output aperture of the hollow cathode to the anode grid 3, and some of the electrons enter the cavity of the main anode 5 and go to the screen grid 4. When the potential is positive relative to the grids 3 and 4, the electrons injected into the cavity of the plasma generator acquire additional energy and begin to ionize the gas. As a result, a dense plasma is generated in the cavity, from which ions are extracted through the holes in the screen electrode.

Tests of a prototype plasma ion emitter were carried out using an electrode system, the length and diameter of the hollow cathode of which were equal to 130 mm, the diameter of the hollow main anode was 130 mm, and the length was 100 mm. The diameter of the exit aperture of the hollow cathode was 10 mm. The magnetic field induction at the poles of the magnetic system was 0.1 T. The flow of argon entering the cathode cavity was 20 cm ³ / min. The discharge current in the continuous mode of burning the discharge reached 1 A, the voltage of the burning discharge was about 400-500 V. The uneven distribution of the ion current density over the surface of the screen grid, estimated by the probe method by the value of the saturation current of ions from the plasma, did not exceed 10% on a diameter of 80 mm . The ion current to the screen grid was 250 mA at a plasma cathode current of 600 mA and the negative voltage at the grid of 200 V. Accordingly, the discharge efficiency, estimated based on the value of the ion current to the screen grid in the region of a uniform plasma, was about 0.5-0.7 A / kW, the energy efficiency of the source, taking into account the transparency of the screen mesh, is about half as low. The calculated values of the efficiency, taking into account the power losses in the plasma cathode, are comparable in magnitude with the characteristic values of the efficiency for technological sources of wide beams based on thermal cathodes, if the energy costs of heating the cathodes are taken into account when calculating the efficiency of the latter.

The simplicity and reliability of the proposed ion source allows its efficient use in ion-beam technologies, in particular, based on the use of chemically active gas beams. Increasing the efficiency of tone extraction will reduce the specific energy costs and reduce the thermal load on the electrodes. As a result, the functional and operational characteristics of ion sources will significantly improve.

Sources of information

1. H. R. Kaufman, J. J. J. Cuomo, and J. M. E. Harper, J. Vac. Sci. Technol. 21, 725 (1982).

2. Y. Oka, T. Shoji, T. Kuroda, O. Kaneko, and A. Ando, Rev. Sci. Instrum. 61, 1256 (1990).

3. Y. Hakamata, T. Iga, K. Natsui, and T. Sato, Nucl. Instrum. Methods B 37/38, 143 (1989).

4. E. Oks, A. Vizir, and G. Yushkov, Rev. Sci. Instrum. 69, 853 (1998).

Claims (1)

An ion source with a cold cathode, containing a plasma cathode, the electrode system of which includes a hollow glow-discharge cathode, a firing electrode and a fine-grained anode grid mounted opposite the hollow cathode outlet, and a plasma generator including a main anode and a screen grid with holes for extracting ions, electrically connected to the anode grid and at a negative potential relative to the main anode, characterized in that the main anode is in the form of a hollow electrode, on the surface ti is established system of magnets for generating a multipole peripheral magnetic field.